The present invention relates to a pump turbine using a runner to work as a pump and a turbine by changing the rotational direction of the runner, a method of controlling said pump turbine, and a method of stopping said pump turbine.
Generally, the runner of a pump turbine, especially a high head pump turbine, is designed so as to realize a sufficient centrifugal pump action to obtain a high head during pump running.
However, this design adversely affects the turbine operation of the pump turbine. Especially when so-called S-characteristics appear as an example, it is considered to be difficult to avoid them perfectly.
It has been recognized that the S-characteristics are a bottleneck especially for high-head pump turbines in civil designing of upstream and downstream waterways, heights of installation elevation of pump turbines, and so on. Therefore, there have been various proposals to control such S-characteristics. For example, Japanese Non-examined Patent Publication S53-143842 (1988) proposes a method of temporarily opening guide vanes of a pump turbine while the running point of the pump turbine is moving along a flowrate decreasing direction on the S characteristics after a load rejection and quickly closing the guide vanes when the running point of the pump turbine starts to move along a flowrate increasing direction on the S characteristics or when the flowrate becomes almost zero, as shown in the accompanying FIG. 1.
However, this proposal is designed to reduce the rotational speed (which temporarily increased after a load rejection) straight down to a predetermined rotational speed or its vicinity which is determined by a governor setting. For this purpose, the temporarily-opened guide vanes are closed as quickly as the sudden closing after a load rejection instead of using the so-called buckling manner which changes limitation of the closing speed of the guide vanes from the xe2x80x9cfastestxe2x80x9d rate to a xe2x80x9cslowxe2x80x9d rate when the opening of the guide vanes Y is smaller than Ya. This is very dangerous in case the S-characteristics controller is disabled. Further this proposal assumes that the temporarily-opened guide vanes start to close when the flowrate starts to increase (from the end of decreasing) or when the flowrate becomes almost zero. However, it is very difficult to detect a flow rate finely (at high resolution) and timely in the transient status of the pump turbine. Even if a high-resolution flowrate is detected, it is very difficult to suddenly reverse the operation of the guide vanes and it can be easily inferred that the guide vanes are opened too much. Particularly, when you keep on operating the guide vanes even after the running point on the S characteristics ends moving along the flowrate decreasing direction and starts to move along the flowrate increasing direction, the influence by the S characteristics may be greater.
Judging from the above, it can be inferred that the method in accordance with Japanese Non-examined Patent Publication S53-143842 (1988) cannot assure the steady performance in case a plurality of pump turbines share an identical penstock or particularly when the flowrate of a pump turbine changes variously not only by its own running status but also by mutual hammering by other pump turbines.
An object of the present invention is to provide a stable pump turbine capable of suppressing water hammer phenomena and other transient influences from the S-characteristics at a load rejection which the conventional pump turbines cannot solve.
The present invention is characterized by a pump turbine which solves the above problem. The present invention is also characterized by controlling a governor to increase a target rotational speed of the runner after a load rejection which shuts off power generated by its generator, generator motor.
The present invention is also characterized by providing a governor designed to detect the rotational speed of the runner and control a discharge regulator such as guide vanes to get a predetermined rotational speed of the runner constantly and controlling the governor to make the target rotational speed only at the transient status immediately after a load rejection substantially higher than the target rotational speed at the steady status in case of the occurrence of a load rejection which shuts off power generated by a generator motor.
The present invention is also characterized by building up a system to increase and correct the preset rotational speed of the governor in the transient status immediately after a load rejection.
Further, the present invention is characterized by building up a system to increase and correct the preset rotational speed of the governor as the rotational speed increases immediately after a load rejection.
Further, the present invention is characterized by building up a system to increase and correct the target rotational speed as the rotational speed increases immediately after a load rejection, to gradually release (or decrease) the correction control after the rotational speed starts to go down, and to release the correction control substantially completely in the steady status.
Further, the present invention is characterized by building up a system to increase the preset rotational speed a little below and along the increasing speed curve while the rotational speed is increasing immediately after a load rejection.
The governor of the pump turbine in accordance with the present invention comprises a closing speed limiter which limits the closing speed of the discharge regulator according to the opening of the discharge regulator. If the closing speed limiter is designed to limit the closing speed of the discharge regulator to a second predetermined value or less which is comparatively higher while the opening of the discharge regulator is larger than a first predetermined value and to a third predetermined value or less which is comparatively lower after the opening of the discharge regulator is smaller than the first predetermined value, the correction control must not block the natural closing action of the discharge regulator by the governor until the opening of the discharge regulator is larger than the first predetermined value at least immediately after a load rejection.
After a load rejection, the present invention closes the discharge regulator when the opening of the discharge regulator is higher than the first predetermined value and temporarily opens the discharge regulator after the closing speed of the discharge regulator is once transferred below the third predetermined value in spite of a Closing command being given from the governor.
The present invention is also characterized by temporarily opening the discharge regulator by correction-control when the rotational speed stops increasing and starts decreasing after a load rejection. (The rotational speed value at this point is called a first peak value.)
In the present invention, the opening of the discharge regulator is made greater temporarily by the correction-control when the rotational speed starts to go down over this peak after a load rejection and consequently, the rotational speed stops decreasing and starts increasing at a much higher value than a natural target value in the steady status given by the governor. (The rotational speed value at this point is called a first bottom value.)
In other words, in the present invention, the opening of the discharge regulator is made greater temporarily by the correction-control when the rotational speed starts to go down over the first peak after a load rejection. This temporary opening operation continues to an inflection point at which the rotational speed curve turns from a convex curve to a concave curve. As the result, the rotational speed stops going down and starts going up at this much higher value than a natural target value in the steady status given by the governor. (The rotational speed value at this point is called a first bottom value.)
The present invention is characterized by starting the temporary opening operation of the discharge regulator by the correction-control before the rotational speed reaches the first peak value after a load rejection, continuing the operation to an inflection point at which the rotational speed curve turns from a convex curve to a concave curve after the first peak, and consequently stopping the decrease of the rotational speed and restarting the increase at the much higher value than a natural target value in the steady status given by the governor. (The rotational speed value at this point is called a first bottom value.)
The rotational speed increases again after the first peak value, stops increasing, and decreases again. (The rotational speed value at this point is called a second peak value.) The present invention is characterized by setting a correction-control releasing rate so that the second peak value may be lower than the first peak value.
The rotational speed decreases again after the second peak value, stops decreasing, and increases again. (The rotational speed value at this point is called a second bottom value.) The present invention is characterized by setting a correction-control releasing rate so that the second bottom value may be lower than the first bottom value.
The present invention is also characterized by correction-controlling the governor to substantially increase the target rotational speed according to the increase of the rotational speed immediately after a load rejection, and gradually releasing correction-control (or decreasing the rotational speed when the rotational speed starts to go down after the first peak, and releasing the correction control substantially completely in the steady status.
The governor of a pump turbine in accordance with the present invention comprises means for detecting a rotational speed, means for setting a target rotational speed, arithmetic means for entering a signal of a difference (which is called a Speed Difference signal) between a target speed signal from the target rotational speed setting means and an actual speed signal from the rotational speed detecting means and outputting an Opening command signal to the discharge regulator, and means for amplifying the signal coming from the arithmetic means and controlling the discharge regulator. The governor further comprises means (which is called a corrector) for entering a speed signal and outputting a signal to substantially correct the target speed command signal to the governor.
The present invention is characterized by comprising a first arithmetic unit which passes a rotational speed signal only when the rotational speed exceeds a fourth predetermined value, a second arithmetic unit which receives a signal output from the first arithmetic unit and outputs a signal (a target signal) which increases while the received signal is increasing in comparatively quick response to the received signal and decreases slowly when the received signal starts to decrease in comparatively slow response to the received signal, and a corrector which receives a signal (a target signal) from the second arithmetic unit and outputs the signal to the governor to substantially correct the target speed command signal.
The present invention is characterized in that the fourth predetermined values is well greater than the maximum rotational speed which can be obtained in the normal operation in an electric power system to which the generator motor is connected.
In the present invention, the second arithmetic unit makes a first order lag response of a comparatively short time constant while a signal output from the first arithmetic unit is increasing and/or a first order lag response of a comparatively long time constant while a signal output from the first arithmetic unit is decreasing.
In the present invention, the second arithmetic unit makes a first order lag response of a comparatively short time constant while a signal output from the first arithmetic unit is increasing and/or an attenuating response of a time constant which is longer than that of a signal before the signal starts to decrease while a signal output from the first arithmetic unit is decreasing.
In case the arithmetic means of the governor is of the PID arithmetic type (P for proportion, I for integration, and D for differentiation), the present invention is also characterized by adding correction signals prior to all P, I, and D operations.
Further, in case the arithmetic means of the governor is of the PID arithmetic type (P for proportion, I for integration, and D for differentiation), the present invention is characterized by adding correction signals to have effects only upon P and I operations.
Further, the present invention is characterized by adjusting a correction signal level so that the temporary opening of the discharge regulator may start in spite of a Closing command signal from the governor earlier than the increase of the rotational speed immediately after a load rejection stops.
Furthermore, the pump turbine of the present invention comprises a first governor which monitors the rotational speed of the runner in the Power Generation mode and controls the discharge regulator to settle the rotational speed of the runner to a predetermined value in any steady state and a second governor which controls the discharge regulator in place of the first governor upon a load rejection of the generator motor. The present invention is characterized by setting the target rotational speed of the second governor substantially higher than the target rotational speed of the first governor in the transient status at least just after a load rejection.
The present invention is characterized by suppressing a reverse water flow upon a load rejection which shuts off electric power generated by the generator motor.
The present invention is characterized in that the rotational speed of the runner does not go down so quickly as in the case of the conventional governor to a value preset by the governor in the transient status after a load rejection which shuts off electric power generated by the generator motor.
The present invention is characterized in that the rotational speed of the runner does not go down to a value preset by the governor upon a load rejection which shuts off electric power generated by the generator motor.
The present invention is characterized by suppressing a reverse water flow in the transient status after a load rejection which shuts off electric power generated by the generator motor.
The pump turbine of the present invention is characterized by suppressing a reverse water flow upon a load rejection which shuts off electric power generated by the generator motor.
The pump turbine of the present invention is characterized in that the rotational speed of the runner does not go down to a value preset by the governor in such a short time for the rotational speed to increase to the first peak value after a load rejection or similar.
Further the present invention is characterized by providing a correction controller which interrupts control by the governor upon the discharge regulator when the rotational speed starts to go down at the peak after the rotational speed quickly increases just after a load rejection in the Power Generation mode in order to temporarily cause the discharge regulator to open while the closing control by the governor is in progress and adjusting the correction control to temporarily increase the rotational speed so that the rotational speed may not go straight down from the peak value to a value predetermined by the governor or its vicinity at least upon full load rejection.
The present invention is also characterized by stopping correction control at the latest when the rotational speed starts to increase and returning control to the governor to adjust the discharge regulator.
The correction control to temporarily open the discharge regulator starts when the rotational speed after a load rejection starts to decrease and continues to a point (inflection point) where the rotational speed curve changes from a convex curve to a concave curve.
Next, the correction control to temporarily open the discharge regulator starts just before the rotational speed starts decreasing after a load rejection and continues to a point (inflection point) where the rotational speed curve changes from a convex curve to a concave curve in the rotational speed decreasing stage.
In the present invention, the correction-control is made to stop the first decrease of rotational speed after a full load rejection at a rotational speed point which is above one third of the difference between the rated rotational speed (or the natural target rotational speed of the governor) and the peak rotational speed value) and, instead, to increase the rotational speed from there.
Further in the present invention, the correction-control repeats the set of decreasing, stopping, and increasing of the rotational speed several times before the rotational speed after the full load rejection is brought down to a value preset by the governor (the natural target rotational speed of the governor).
The governor in accordance with the present invention comprises a closing speed limiter which limits the rate of closing the discharge regulator according to the opening of the discharge regulator. In case the closing speed limiter is designed to limit the closing speed of the discharge regulator to a second predetermined value or below which is comparatively high when the opening of the discharge regulator is a first predetermined value or above or to limit the closing speed of the discharge regulator to a third predetermined value or below which is comparatively low when the opening of the discharge regulator is a first predetermined value or below, the correction-control is disabled as long as the opening of the discharge regulator is above the first predetermined value.
After a load rejection, the rotational speed first decreases, turns at a point (a first bottom speed value) to increase by the correction-control, and then turns at another point (a second peak speed value) to decrease. The correction-control adjusts to make the second peak value lower than the first peak value.
Next, the rotational speed decreases after the second peak value, gradually stops decreasing, and turns at a point (a second bottom speed value) to increase. The correction-control adjusts to make the second bottom value lower than the first bottom value.
The governor of a pump turbine in accordance with the present invention comprises means for detecting a rotational speed, means for setting a target rotational speed, arithmetic means for entering at least a signal of a difference (which is called a Speed Difference signal) between a target speed command signal from the target rotational speed setting means and an actual speed signal from the rotational speed detecting means and outputting an opening command signal to the discharge regulator, and means for amplifying the signal coming from the arithmetic means and controlling the discharge regulator. The governor further comprises means (which is called a correction-controller) for entering at least a rotational speed signal, and means for correcting substantially the signal from the arithmetic means.
The correction-controller further comprises a first arithmetic unit which allows a rotational speed signal to pass only when the rotational speed exceeds a fourth predetermined value, a second arithmetic unit which receives a signal output from the first arithmetic unit and outputs a signal (a target signal) which increases quickly in comparatively quick response to the received signal while the received signal is increasing and decreases slowly in comparatively slow response to the received signal when the received signal starts to decrease, a comparator which compares the target signal and the signal output from the first arithmetic unit and outputs the result (a difference), a first limiting element which limits the positive component of the signal output from the comparator, a differential element which incompletely differentiates the signal output from the first limiting element, and a second limiting element which blocks the negative components of a signal output from the differential element and limits the positive components of the signal at a predetermined value.
In the present invention, the fourth predetermined value is well greater than the maximum rotational speed which can be obtained in the normal operation on an electric power system to which the generator motor is connected.
The present invention is also characterized by providing a second arithmetic unit which makes a first order lag response of a comparatively short time constant while a signal output from the first arithmetic unit is increasing or an attenuating response of a time constant which is longer than that of a signal before the signal starts to decrease while a signal output from the first arithmetic unit restarts to decrease.
The present invention is also characterized by providing a correction-control which is designed to determine the signal output timing according to actual transitions of the rotational speed and keep the output value constant between starting and resetting thereof.
Further, the correction-control of the present invention is designed to work only when the rotational speed is over a fifth predetermined value which is higher than a target value in the steady status and is disabled in the other status.
In case of emergency, to immediately stop the pump turbine running in the Power Generation mode, the pump turbine of the present invention fully closes the discharge regulator and stops the revolution of the pump turbine with both the governor and the correction-control operative at least initially in the emergency stop process.
Further, in case of emergency, to immediately stop the pump turbine running in the Power Generation mode, the pump turbine of the present invention first attenuates the unwanted influence of the S characteristics, fully closes the discharge regulator, and stops the revolution of the pump turbine with both the governor and the correction-control operative initially in the emergency stop process.
To solve the above problems, the present invention causes the discharge regulator to repeat the close and open operations several times to stop water flowing through the runner.
In the present invention, closing of the discharge regulator proceeds step by step as the closing and opening operations of the discharge regulator are repeated after a load rejection.
Further, the discharge regulator is made to temporarily open at least once before the decreasing rate of the rotational speed of the runner becomes a maximum after the first peak upon a load rejection. The governor is controlled to suppress a counterflow of water in the transition status after a load rejection.
Similarly, the discharge regulator is made to temporarily open at least once before the decreasing rate of the rotational speed of the runner becomes a maximum after the first peak upon a load rejection. The governor is controlled to make the rate of decrease of the rotational speed of the runner much smaller than the rate of increase thereof.
Further similarly, the discharge regulator is made to temporarily open at least once before the decreasing rate of the rotational speed of the runner becomes a maximum after the first peak upon a load rejection. The governor is controlled to eliminate a second water hammer peak in the upstream side of the turbine which is observed just after the rotational speed of the runner starts to decrease upon a load rejection according to the conventional governor.
A correction signal generator is also provided to supply correction values to the governor to make the rate of decrease of the rotational speed of the runner much smaller than the rate of increase of the rotational speed after a load rejection.
A correction signal generator is also provided to supply correction values to the governor to eliminate the second water hammer peak in the upstream side of the turbine which is observed immediately after the rotational speed of the runner starts to decrease after a load rejection.
A correction signal generator is also provided to supply correction values to the governor to eliminate the second water hammer peak in the upstream side of the turbine which is observed immediately after the rotational speed of the runner starts to decrease after a load rejection.
Further, the discharge regulator is made to temporarily open at least once before the decreasing rate of the rotational speed of the runner becomes a maximum after the first peak upon a load rejection. The governor is controlled to adjust the correction-control so that the maximum water pressure in the upstream pipe may be limited to be approximately constant around the first peak of the rotational speed.
A correction signal generator is also provided to supply correction values to the governor to correct the output signal of the governor. Upon a load rejection, the correction signal generator outputs a correction value to make the rate of decrease of the rotational speed of the runner much smaller than the rate of increase of the rotational speed.
A correction signal generator is also provided to supply correction values to the governor to correct the output signal of the governor. The correction signal generator corrects signals of the governor to eliminate the second water hammer peak in the upstream side of the turbine which is observed immediately after the rotational speed of the runner starts to decrease after a load rejection.
A correction signal generator is also provided to supply correction values to the governor to correct the output signal of the governor. The correction signal generator corrects the output signals of the governor to eliminate the second water hammer peak in the upstream side of the turbine which is observed immediately after the rotational speed of the runner starts to decrease after a load rejection.